There are various ways of packaging a plurality of integrated circuit dies in a single electronic device. Referring to FIG. 1, in a first example according to the prior art, an electronic device 10 comprises first and second integrated circuit dies 11, 12 mounted side by side on a substrate 13. The first and second integrated circuit dies 11, 12 are provided on the substrate 13 in a housing 14 and the substrate 13 is mounted on a printed circuit board (PCB) 15.
Electrically conductive elements 16 extend through the substrate 13 from a surface of the substrate 13 facing the first and second integrated circuit dies 11, 12 to a surface of the substrate 13 facing the PCB 15. Electrically conductive bumps 17 are provided on surfaces of the first and second integrated circuit dies 11, 12 facing the substrate 13 and the first and second integrated circuit dies 11, 12 are positioned such that the electrically conductive bumps 17 are each in contact with a respective one of the electrically conductive elements 16. The substrate 13 has solder balls 18, forming a so-called ball grid array, on the surface of the substrate 13 facing the PCB 15, the solder balls 18 each being in contact with a respective one of the electrically conductive elements 16. The PCB 15 has electrically conductive tracks 19 and the substrate 13 and the PCB 15 are positioned such that the solder balls 18 are each in contact with a respective one of the electrically conductive tracks 19. Some of the electrically conductive tracks 19 of the PCB 15 are arranged to couple the first and second integrated circuit dies 11, 12 to other electronic devices (not shown) and others are arranged to couple the first and second integrated circuit dies 11, 12 to one another. Only a subset of the electrically conductive elements 16 and electrically conductive tracks 19 typically required are shown in FIG. 1 for clarity.
A problem with the electronic device 10 shown in FIG. 1 is that placing the first and second integrated circuit dies 11, 12 side by side increases the width of the electronic device 10. In particular, increases in the size of the substrate 13 and the PCB 14 increase the size and cost of the electronic device 10 such that the electronic device 10 is not suitable for many applications.
Referring to FIG. 2, in a second example according to the prior art, an electronic device 20 similar to the electronic device 10 of the first example has the second integrated circuit die 12 mounted on top of the first integrated circuit die 11. In other words, the first integrated circuit die 11 is mounted on the substrate 13 and the second integrated circuit die 12 is mounted on a surface of the first integrated circuit die 11 facing away from the substrate 13. For the second integrated circuit die 12, instead of the electrically conductive bumps 17 being provided on the surface facing the substrate 13, wires 21 are provided that extend from the surface facing away from the substrate 13 to the electrically conductive elements 16 of the substrate 13. This allows the first and second integrated circuit dies 11, 12 to be packaged in the electronic device 20 without any a significant increase in the width of the electronic device 20. However, the coupling of the second integrated circuit 12 to the conductive elements 16 of the substrate 13 by the wires 21 is not ideal. Provision of the wires 21 typically involves slower and more expensive manufacturing processes than providing the electrically conductive bumps 17. The length of the electrical path provided by the wires 21 is typically much longer than the length of the electrical path provided by the electrically conductive bumps 17, which means that the electrical performance of components coupled by the wires 21 is reduced. Also, the electrically conductive bumps 17 tend to provide improved thermal conductivity in comparison to the wires 21, with the result that the first and second integrated circuit dies 11, 12 can be cooled more effectively when the electrically conductive bumps 17 are used for electrical coupling rather than the wires 21.
Referring to FIG. 3, in a third example according to the prior art, an electronic device 30 similar to the electronic device 20 of the second example has the second integrated circuit die 12 mounted on an additional substrate 31 between the first and second integrated circuit dies 11, 12. In other words, the second integrated circuit die 12 is mounted on the additional substrate 31 and the additional substrate 31 is mounted on the surface of the first integrated circuit die 11 facing away from the substrate 13. This allows the second integrated circuit die 12 to retain its electrically conductive bumps 17, as in the first example. The additional substrate 31 has electrically conductive elements 32 extending through it from a surface of the additional substrate 31 facing the second integrated circuit die 12 to a surface of the additional substrate 31 facing the substrate 13 of the electronic device 30 that is also present in the first and second examples, now referred to as the main substrate 13. Additional solder balls 33 are provided on the surface of the additional substrate 31 facing the main substrate 13. The additional solder balls 33 are each in contact with a respective one of the electrically conductive elements 32 of the additional substrate 31, and the additional substrate 31 and the main substrate 13 are positioned such that the additional solder balls 33 are also in contact with the electrically conductive elements 16 of the main substrate 13. A problem with the electronic device 30 of the third example is that the provision of the additional substrate 31 adds to the expense of the electronic device 30. The size of the electronic device 30 is also increased by the provision of the additional solder balls 33 and the additional substrate 31 and, in particular, the height of the electronic device 30 may not therefore be acceptable in some applications.